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<h1>Gear template generator help</h1>
The <a href="http://woodgears.ca/gear/"><b>gear template generator</b></a> 
is a program to calculate and print<br>
gear shapes for involute spur and pinwheel gearing.
<p><br>
A <a href="index_fr.html"><b>French translation</b></a> of this document is also available,
however, the program itself is only in English.
</table>

<h3>Gear type and properties</h3>
<img src="main_tab.png" width=402 height=196><p>

<h4>Tooth spacing</h4>
<p class="cat">Specifies the center to center tooth spacing,
as measured along the gear's pitch diameter.

<h4>Type</h4>
<p class="cat">
This selects what type of gear teeth to draw.
The gear's teeth can be spur, pinwheel, or protractor.
</p>
<h4>Involute</h4>
<p class="cat">
This specifies involute spur gears.  Involute spur gears are
the most commonly used type of gear.  Any two gears that have
the same tooth spacing (or pitch) and the same contact angle (also known as pressure angle)
will mesh and run smoothly.
</p>
<img src="pinwheel.png" align=right>
<h4>Pin</h4>
<p class="cat">
For some applications, it is desirable that one gear be comprised of just
a ring of pins.  Such gears are also known as "lantern" gears.  The pins are typically
held together by two discs on either side, so that the whole structure could be said
to look like a "lantern".  Such a gear may or may not have a shaft passing through
the middle of the pins.
</p><p class="cat">
The primary advantage of this type of gear is that it's possible to make gears with
as few as three teeth that will still run smoothly.
</p><p class="cat">
For pinwheel gearing, the gear on the right will always be the pinwheel and
the gear on the left will always be cycloid shaped to mate with the pinwheel.
</p>
<img src="protractor.png" align=right>
<h4>Protractor</h4>
<p class="cat">
Sometimes it's useful to be able to create a template that divides a circle into a
specific number of intervals.  For example, to divide a circle into 23 equal parts 
with a protractor would be tedious and error prone.  Using this program
you can print a template that divides the circle as specified.
</p>

<h4>Shaft spacing</h4>
<p class="cat">
This field always displays the calculated shaft spacing value.  The shaft spacing
is the sum of the pitch radii of both gears.  Pitch radius is calculated from the
pitch circumference.  Pitch circumference is equal to the number of teeth times the
tooth spacing.
</p><p class="cat">
You can also enter a new value in this field and the gear's tooth spacing will automatically
be recalculated to produce the desired center to center distance for the two gears.
</p>
<h4>Contact angle</h4>
<p class="cat">
This field specifies the contact angle, also known as pressure angle, for involute spur
gears.  Larger pressure angles produce gears that have more triangular looking teeth.  Larger
pressure angles work better for gears with a small number of teeth, but the overall result
is lower efficiency due to higher friction in the gear set.
</p>
<p class="cat">
This field is only applicable for involute spur teeth and is hidden if other types
of gear teeth are selected.
</p>
<h4>Pin diameter</h4>
<p class="cat">
This field specifies the size of the pins for pinwheel gearing.  This field is only applicable
to pinwheel gearing and is hidden if other types of gear teeth are selected.

<h3>Gear ratio</h3>
I have had nuerous requests to make the gear program display ghe gear ratio.
The reason the program does not explicitly display the gear ratio is that 
<b>the gear ratio is whatever you enter</b>.  
For example, if you have a tooth count
of 7 and 12, the gear ratio is 7:12.  That is to say, the 7-tooth gear will
turn 12 times for every 7 turns of the 12-tooth gear.  Similarly, a 10-tooth
with a 30-tooth gear will have a gear ratio of 30:10, which can also be epxressed
as 3:1.

<h3>Gear properties</h3>
<img src="gear_properties.png" width=183 height=103 align=left>
This section allows you to specify the parameters specific to each gear.
<br clear=left><p>
<h4>Show</h4>
<p class="cat">Selects whether the gear is visible.
Note that for pinweel gears, the properties of the pinwheel affect 
the shape of the mating gear, so even if the right gear is hidden, its properties
still affect the gear on the left.
</p>
<h4>Spur</h4>
<p class="cat">
Selects a regular spur gear.  That is, a round gear with teeth on the outside.
</p>
<h4>Ring</h4>
<p class="cat">
Selects a ring gear.  A ring gear is a gear with teeth on the inside.
Ring mode can only be selected if the other gear is a spur gear.  Ring gears are useful
when making <a href="http://woodgears.ca/gear/planetary.html">planetary gear sets</a>
</p>
<h4>Rack</h4>
<p class="cat">
Selects a "rack" type gear.  A rack is essentially a gear that has been unwrapped.
Rack and pinion mode is only currently available for involute tooth types.
</p>
<h4>Teeth</h4>
<p class="cat">
Specifies the number of gear teeth.
</p>
<p class="cat">
<table align=right><td width=220>
  <img src="asymetric_addendum.png" width=216 height=191><br>
  <b><small>Odd shaped gears generated by setting the right side gear addendum to zero.</small></b>
</table>
<h4>Addendum</h4>
Specifies the addendum of the teeth.  The addendum is how much the gear tooth protrudes
outside its pitch diameter.  It is specified relative to the tooth spacing.  That is,
a setting of 0.25 means that a tooth's addendum will be one quarter of the spacing, or
about half of its width.
<br><br>
The gear's dedendum (that is, how deep a cut beyond the pitch circle between teeth)
is taken from the mating gear's addendum.  So to set the dedendum of a gear, just
set the corresponding addendum of the mating gear.
<br><br>
Note that cycloid gears don't use the addendum parameters.
</p>

<h3>Spokes & more tab</h3>
<img src="spokes_tab.png" width=399 height=193><p>

<h4>Diametric pitch</h4>
<p class="cat">
Some people prefer to use diametric pitch, as opposed to tooth spacing 
(also known as circumferential pitch).
Diametric pitch is equal to the gear's tooth count divided by the pitch diameter,
so this number varies inversely with tooth size.  Please note that version 2
and earlier of the gear generator calculated this as diameter per tooth (inverse
of what it should be).
You can enter a value in the diametric pitch, and the
circumferential pitch on the main tab will automatically be updated.
</p>

<h4>Slop</h4>
<p class="cat">
The amount of total slop, play, or tolerance.
With slop set to zero, the gears are printed so that they fit exactly, with no
tolerance for slop.  Usually, the width of the cut on the bandsaw or scroll saw
will provide enough slop, but you can also add slop by setting this parameter.
</p>


<h4>Pitch diameter</h4>
<p class="cat">
The pitch diameter is the diametric pitch times the number of teeth.  The pitch diameter
is useful for working out gear spacing.  The ideal center to center distance of a pair
of gears is equal to the sum of the pitch diameters, divided by two.  Note that the shaft
spacing in the "Gear properties" tab already shows the center to center distance
as "shaft spacing".
</p>

<h4>Overall diameter</h4>
<p class="cat">
This displays the overall diameter of the gear, from tip to tip.
</p>


<h4>Spokes</h4>
<p class="cat">
Specifies the number of spokes.  Only spur gears above a certain number
of teeth are large enough to have spokes.
</p>


<h4>Shaft hole diameter</h4>
<p class="cat">
Specifies the shaft hole to draw.  For pinwheel (lantern) gears, this specifies the
size of the shaft in the middle of the pins.  The gear teeth of the mating gear
will be kept short enough so as not to interfere with the central shaft.
Specify zero to omit the center shaft or shaft hole.
</p>

<hr>
<h1 id="chain">Chain &amp; Sprocket mode</h1>
The gear template generator version 2.0 includes a "chain and sprocket" mode.
This mode is intended to assist in generating sprocket shapes for wooden block
chains and roller chains.
</p><img src="sprocket_tab.png" width=399 height=195 align=left>
Chain & sprocket mode is turned on by selecting the "Chain & Sprocket" tab on the
bottom left of the main window.
<br clear=left><p>
<table border=0><td>
<img src="sprocket.png" width=246 height=141><br>
<center><b>Block chain</b></center>
<td>
<img src="rollerchain.png" width=223 height=141><br>
<center><b>Roller chain</b></center>
</table>
The gear template generator can produce both block chain sprockets, and roller chain sprockets.
<p>
Nearly all modern metal drive chains, such as those used on bicycles, are of 
the "roller chain" variety.  Roller chains have a cylindrical roller on every pin joint,
with two sets of links on either side to join them together.
<p>
<img src="blockchain.jpg" width=400 height=213 align=left>
Block chains are an older, obsolete style of drive chain.  Block chains are much simpler to make,
and lend themselves well to wood.
In a block chain, the sprocket engages bocks in the middle of the chain.  Each block has two
holes, to which the links on either side attach.  An example use of a wooden block
chain can be seen in this <a href="http://woodgears.ca/tracked_vehicle/index.html">tank thread
vehicle</a>
<br clear=left><p>
<img src="undercut.png" width=322 height=155 align=left>
If the blocks of a block chain are not rounded on the corners, then the corners tend
to scrape the sprocket where the chain engages and disengages the sprocket.
<p>
The gear template generator will generate sprocket shapes that make allowances for this
"undercut" next to the teeth for this, but the sprockets are still somewhat ugly and inefficient.
<br clear=left><p>
<img src="chamfer_undercut.png" width=322 height=183 align=left>
A much better solution is to put a bit of a round or chamfer on the edges of the
chain blocks.  The sprocket at left is very similar to the previous sprocket, but with blocks
that have chamfered corners.  Note that the teeth have much less undercut.
<p>
For clarity, I changed the links to be very thin, but the
links do not actually engage the sprocket, so only the link's length, not its actual
shape contributes to the sprocket shape.

<br clear=left><p>
<img src="three-tooth.png" width=376 height=226 align=left>
The gear generator can generate shapes for workable sprockets down to three teeth.
However, these sprockets are inefficient and will run very rough.  If you use the "Animate"
function in the gear template generator, you can see that the chain has quite a bit of 
side-to-side motion.
<p>
The shape of the teeth also doesn't engage the chain very well, as the teeth need to be
very sloped to allow the chain to engage and disengage the sprocket.

<br clear=left><p>
<img src="eight-tooth.png" width=376 height=173 align=left>
Sprockets with larger number of teeth will run much more smoothly.
<br clear=left><p>


<br clear=left><p>

<img src="no_links.png" width=248 height=166 align=left>
<img src="show_parts.png" width=132 height=57 align=right>
To better see how the chain meshes, parts of the chain and sprocket can be hidden.
The image at left, for example, has the chain links hidden.  You can also hide
the chain entirely.  Hiding the chain is useful when making a printout of the sprocket
template shape to use when cutting the sprocket out of plywood.
<p>
The image at left also has  the "Show pitch diameter" turned on.  The blue lines
represent the pitch diameter, and the lines crossing it indicate the centers of the tooth
undercut radii.  If you have the right size drill, you can start by drilling out the undercut
circles, which will make it easier to cut out the rest of the sprocket with a bandsaw
<br clear=left>
<h3>Specifying the chain dimensions</h3>

<img src="dimensions.png" align=left width=342 height=225>
The shape of the sprocket teeth is generated based on the shape of the chain blocks,
and the length of the chain links.
<p>
The shape of the chain blocks and links is specified in terms of length and width.
Please note that the specified length is the length between the two holes.  The program
automatically adds some length to the link to allow for material around the holes.
<p>
An additional parameter, "Chamfer" determines how much to remove from each corner 
of the blocks and links.
If "Round chamfers" is selected, the chamfer is replaced by a round with a radius
equal to the chamfer measure.
<br clear=left>

<hr>
<h1>Display parameters</h1>
<img src="display_properties.png" width=311 height=194><p>
This part of the panel selects which aspects of a gear to display.
<h4>Show pitch diameter</h4>
<p class="cat">
When selected, a circle is drawn indicating the gear's pitch diameter.
</p>
<img src="line_of_contact.png" align=right>
<h4>Show line of contact</h4>
<p class="cat">
For involute teeth, this shows the contact angle (pressure angle) and base radii
of the two gears.  If you think of the base radii as being two spools, a point
along a string unwound from the right gear's base radius and wound onto the left
gear's base radius would exactly follow the path along which both gears touch.
</p>
<h4>Show center</h4>
<p class="cat">Show a crosshair in the center of each gear.</p>
<h4>Draw thicker lines</h4>
<p class="cat">Doubles the thickness of lines used to draw the gear, so
that the lines snow up better on printouts..</p>
<h4>Grid</h4>
<p class="cat">
Draw a grid.  The grid is useful for getting a sense of scale, for checking that
a printout was scaled correctly, and to help align multiple pages together when
pasting together multi-page printouts.
</p>
<img src="grid_diagonals.png" align=right>
<h4>Grid diagonals</h4>
<p class="cat">
Draw diagonal lines on the grid.  Diagonal lines are very useful to help align
the sheets of a multi-page printout when gluing the pieces of paper together.
The diagonals grids work so well, I later wrote 
<a href="http://woodgears.ca/bigprint">BigPrint</a> to allow other types of 
images to be pasted together this way.
</p>
<h4>Animate</h4>
<p class="cat">
Slowly turn the gears.  This allows you to examine how the gears mesh.
Note that spur gears with less than 10 teeth and low contact angles will often
cause interference.  For gears with very few teeth, try pinwheel gears.
</p>
<h4>Wobbly</h4>
<img src="wobbly_mode.png" align=right>
<p class="cat">
I implemented "wobbly mode" for the evaluation version of the program.  The eval version
can do everything the full version can do, but all output is distorted.  The distorted
gears would not work in real life.
</p><p class="cat">I found the distorted "wobbly mode" fun to watch,
so I have added this "feature" as an option to the full version as well, just for fun.
</p>

<h4>Show rotated</h4>
<p class="cat">
This field causes the gears to be displayed rotated.  The angle is specified
as one hundredths of a tooth.  Specifying 25, for example, will cause the gears to
be rotated by one quarter tooth interval.
</p><p class="cat">
This feature is useful if you want to check that spur gears mesh without interference.
It's especially useful if you use the up/down buttons, and zoom in on the meshing point
by reducing the value of the "screen view width" field.
</p>
<h4>Screen view width</h4>
<p class="cat">
This field indicates how wide an area the screen represents.
This value defaults to 20 cm, or about the width  of the printable region on
a normal piece of paper.
</p><p class="cat">
Note that this value is in whatever units you chose.  If you change the units to "inches"
then the visible region would change to 20 inches, along with all other dimensions.
The display would not change, but when you print it, it will now be much larger as it's
now sized in inches.

</p>


<h3>Saving</h3>
The parameters for a gear can be saved in a file for later reloading.
The parameters are simply stored in a text file.  If a file called "default.gear" exists
in the same directory as the program, it will be loaded automatically when the program starts.

<h3>Units</h3>
Units can be selected to be inches, centimeters or millimeters.
Note that the displayed gear's size does not change if the units are changed.
A gear that is 10 cm across, when you change the units to inches, will now be 10 inches
across.  The screen width would also change from 20 cm to 20 inches.  However, on printing
or exporting, the gears will be scaled accordingly.
Note, however, that on importing DXF, the units are not specified inside the file.  Typically,
one must indicate to the importing program what units are represented in the file.
<p>
<hr>

<h1>Printing</h1>
<img src="print_preview.png" align=right>
The gear template generator is able to print gears that span many pages.
If a gear does not fit onto a single page, then the gear is split across multiple
pages to be printed and then glued together.
<p>
Grid lines, especially when combined with diagonal grid lines, are very useful
to help precisely align the pages when gluing them together.
<p>
It's advisable to do a print preview before printing your gears.  The dimensions you
have specified might result in gears that span a surprisingly large number of pages.


<h3>Printing parameters</h3>
<img src="print_setup.png" width=317 height=366><p>
<h4>Printer scale calibration</h4>
<p class="cat">
You may find that your printer prints just slightly larger or smaller than
it should, especially if your printer is a laser printer.  
If you find that 10 grid lines of a one centimeter grid are actually
10.1 cm horizontally, you can compensate by setting the width calibration
to 99%.  If you switch to "landscape" orientation, the "width" is actually
the length.  The labels adjust to reflect this.
</p>
<h4>Horizontal / vertical / overlap</h4>
<p class="cat">
If you print gears that span multiple pages, the gears are printed with no overlap
by default.  You may prefer to have a slight amount of overlap from page to page 
to give you more confidence in aligning the pages.  
You can either enter the overlap, or you can enter the spacing of the pages.
Note that the spacing and size of the pages always total up to the printable
area on a page.
</p><p class="cat">
You may also find that its quite easy to align the pages even without overlap
when grid diagonals are enabled.                                 
</p>
<h4>Print overlap area</h4>
<p class="cat">
You can select whether to print in the overlapped area.  This option is only
enabled if an actual overlap is selected using the horizontal/vertical/overlap fields.
</p>
<h4>Center gears</h4>
<p class="cat">
Normally, the gears are in the top left of the page, or group of pages.
If you check this, the gears will be centered on the page, or group of pages.
</p>
<h4>Print parameters</h4>
<p class="cat">
If checked, the actual gear parameters will be printed on the top left of the page.
</p>




<hr>
<h3>Exporting</h3>
When exporting to a file, everything that is drawn on the screen is exported.  This
included both gears, as well as any center and grid lines you may have turned on.
It's recommended that you turn off everything but one gear and its center crosshair
before exporting.  Otherwise, it can be difficult to separate the gears from the grid in 
whatever program you are importing into.
<p>
No printer pagination will be applied to export.

<table align=right border=1 cellspacing=0><td><img src="cad_gear.png" align=right><br>
<b><small><center>3D gear drawn from gear outline<br>in Google SketchUp</table>
<h4>DXF (with poylylines)</h4>
Most CAD programs can import DXF files.  The gear template generator's DXF export
is relatively simplistic and only two dimensional, but it will get the shapes 
into your CAD program.
<p>
The DXF export does not include units.  Programs that import DXF typically allow
you to specify which units the DXF file actually uses.  For example, if you used
inches to design your gear, but the importing program assumes the units are
millimeters, the imported gear will be much smaller than you expect.
<p>
Please note that DXF export with polylines is less than perfect, and that
AutoCad will not successfully import this.  Unfortunately, I have no means
of debugging this.  For use with AutoCad, use the basic DXF export.

<h4>DXF (basic DXF)</h4>
DXF is a very difficult to figure out format, and the DXF exported by the
gear template generator may not be compatible with all programs.  If the
"with polylines" export does not work, try exporting as basic DXF.  Basic
DXF exports line segments only.  Unfortunately, this means some programs
will not recognize the outline as a joined object.

<h4>SketchUp</h4>
One of the most popular CAD programs among woodworkers is the free
SketchUp.  However, the free version of 
<a href="http://sketchup.com">SketchUp</a> does not handle DXF import.  
It does, however, import data in "Collada" format.  
Because so many people use the free version of SketchUp, I implemented export 
to this format so that you can still import gears into the free SketchUp.
As CAD programs go, SketchUp is relatively easy.  But be warned.  All CAD programs
have a steep learning curve.
<p>
When you import a gear into SketchUp, it will be imported as nested objects.
Keep opening the objects until you can select individual line segments
of the gear outline.  To turn the
outline into a surface that can be extruded, draw a rectangle around the whole
outline, then delete the outline of the rectangle.  If your gear has spoke
and center holes, select these with a double click, copy them, delete them, then
paste them in place.  After that, you will be able to delete the surface
inside the spoke holes.  I don't think SketchUp works as well as they say it should in
this particular regard, but the above procedure has worked for me.

<h4>HPGL</h4>
HPGL stands for "Hewlett Packard Graphics Language".  It is the format used by
the old HP plotters.  Nobody uses plotters anymore, but the format is fairly
straightforward and various pieces of software still know how to import and export
graphics in this format.
<img src="excel-csv.png" align=right>
<h4>CSV (for spreadsheet)</h4>
CSV (Comma Separated Values) is the simplest form of export, consisting of
just two columns of numbers, plus some annotation.  This format can be loaded
into spreadsheets such as Excel.  You can display the gears as a graph in Excel
by selecting the two columns of numbers and generating an X-Y scatter graph
from the data.
<p>
Displaying gears in a spreadsheet is not particularly useful, but it's a good 
starting point if you wish to manipulate the X-Y points in some way for your own purposes.


<h4>Image (bitmap)</h4>
Exports the image as a bitmap (BMP, Jpeg, or PNG).  A window will pop up
allowing you to specify how many pixels per size unit (pixels per inch, per centimeter
or per millimeter), and whether antialiasing (line smoothing) is turned on.

<h4>PDF</h4>
The PDF export is intended for importing into laser cutters and such.
The "page size" used is whatever is needed to print the gear.  PDF export
does not split the output across multiple pages.
<p>
If you need to create a PDF for printing across multiple pages on another printer,
the best way to proceed is to print to a file.  To print to a file,
go to "configure printer" under print setup, and select "Microsoft XPS document..."
as the printer.  Then print.  Windows will prompt you to specify a file
to print to.  Then upload the XPS file to <a href="https://xps2pdf.co.uk/">
http://www.xps2pdf.org/</a> to convert it to a PDF file.  Note that this
trick works with any program that can print to a printer.  No need to install 
special software on your computer to create PDF files.  There are also
"printer drivers" available on the internet that allow you to print directly 
to a PDF file on your computer, such as the free 
<a href="http://www.bullzip.com/products/pdf/info.php">Bullzip PDF printer driver</a>
, but printing to XPS and then converting doesn't 
require any extra software installation.

<br>
<h3>Any other questions?</h3>
If you have any questions about the gear template generator that this Help doesn't
answer, feel free to email.  Feedback is always appreciated.  My email address is:<br>
&nbsp; &nbsp;<img src="addr.png" width=170 height=16 align=middle>
<p>
More about the <a href="http://woodgears.ca/gear/"><b>Gear template generator</b></a>


</table>
